CS378 -Mobile Computing. Intents

Transcription

1 CS378 -Mobile Computing Intents

2 Intents Allow us to use applications and components that are part of Android System and allow other applications to use the components of the applications we create Examples of Google applications:

3 Four Primary Application Components Activity single screen with a user interface, app may have several activities, subclass of Activity Service Application component that performs longrunning operations in background with no UI Content Providers a bridge between applications to share data Broadcast Receivers component that responds to system wide announcements

4 Activation of Components 3 of the 4 core application components (activities, services, and broadcast receivers) are started via intents intents are a messaging system to activate components in the same application and to start one application from another

5 AndroidManifest.xml Recall the manifest is part of the application project. The manifest contains important data about the application that is required by the Android system before the system will run any of the application's code common error: have Activity in application that is not included in manifest runtime error when application tries to start Activity not declared in manifest

6 AndroidManifest.xml Purpose contains Java package name of application - unique id for application describes components of application: activities, services, broadcast receivers, content providers and intent messages each component can handle declares permissions requested by application minimum required API level libraries application to link to

7 AndroidManifest.xml -Launcher Intent Declare this as Activity to start when application started

8 Intent Class and Objects android.content.intent passive data structure description of action to performed or if created by a broadcast, a description of something that has happened and is being announced to broadcast receivers Intent objects carry information, but do not perform any actions themselves

9 Intents and App Components Intent to Launch Activity or change purpose of existing Activity Context.startActivity() Activity.startActivityForResult() Activity.setResult() Intent to Initiate Service or give new instructions to existing Service Context.startService() Context.bindService() Intents intended for Broadcast Receivers Context.sendBroadcast() Context.sendOrderedBroadcast() Context.sendStickyBroadcast() The Android System finds the right application component to respond to intents, instantiating them if necessary.

10 Intent Object Information component name (of desired component) action (to execute) data (to work on) category (of action) type (of intent data) extras (a Bundle with more data) flags(to help control how Intent is handled)

11 Intent Object Info-Component data for the component that receives the intent action to take data to act on data for the Android system category of component to handle intent (activity, service, broadcast receiver) instructions on how to launch component if necessary

12 Intent Info -Component Component name that should deal with Intent fully qualified class name of component and the package name set in the manifest file of the application where the component resides optional! if not provided Android system uses resolves suitable target name is set by setcomponent(), setclass(), or setclassname()

13 Intent Info -Action Name Action desired (or for broadcast intents, the action / event that took place) Many actions defined in Intent class Other actions defined through the API example, MediaStore class declares ACTION_IMAGE_CAPTURE and ACTION_VIDEO_CAPTURE You can define your own Intent Action names so other applications can activate the components in your application

14 Intent Action Name Action acts like a method name determines what rest of data in Intent object is and how it is structured, especially the data and extras setaction() and getaction() methods from Intent class

15 Intent Action

16 Intent Info-Data URI (uniform resource identifier) of data to work with / on for content on device a content provider and identifying information, for example an audio file or image or contact MIME (Multipurpose Internet Mail Extension, now internet media type) initially for types, but extended to describe type information in general about data / content image/png or audio/mpeg

17 Intent Info -Category String with more information on what kind of component should handle Intent

18 Intent -Extras A Bundle (like a map / dictionary, keyvalue pairs) of additional information to be given to the component handling the Intent Some Action will have specified extras ACTION_TIMEZONE_CHANGED will have an extra with key of "time-zone" (documentation is your friend) Intent method has put methods or put a whole Bundle

19 Example Use an Intent so app asks camera to take picture and displays the resulting picture important details: permission to write and read (JellyBean) to and from SD card getting file names correct reduce size of original image

20 IntentExample

21 LinearLayoutwith button ImageView Layout ImageViewinitially displays default Image button click results in call to takephoto android:onclick attribute set

22 takephotoin IntentExampleActivity

23 Clicking button starts Camera Activity IntentExamplewill be stopped recall Activity lifecycle, play well with others Result when picture taken return to IntentExampleactivity

24 onactivtyresult when camera app checks Android system will call this method (callback) look at result and take appropriate action verify our requested action was completed

25 onactivtyresult

26 Intent Resolution How does the Android system determine what component should handle an Intent? explicit Intent designates target component by name typically used for inter application messaging and activity starting recall, LifeCycleTest

27 Intent Resolution -Implicit component name is blank (unknown) typically used when starting component in another application Android system uses data from Intent (action, category, data) and tries to find / match best component for job Uses Intent Filters

28 Intent Filters Applications and components that can receive implicit Intents advertise what they can do via Intent Filters components with no Intent Filters can only receive explicit Intents typical of many activities activities, services, and broadcast receivers can have one or more intent filters

29 Intent Filters Android system should know what application can do without having to start the component before runtime exception is Broadcast Receivers registered dynamically; they create IntentFilterobjects at runtime intent filters generally declared as element of applications AndroidManifest.xml file

30 IntentFilter-Example filter declares action, category, and data

31 IntentFilter-Example The Android system populates the application launcher via IntentFilters